The basis for formulating so-called “uniform” emission standards for motor vehicles is examined and found to be inconsistent with the widely accepted principle that “the polluter should pay,” if consideration is given to the problems caused by pollution rather than the sources of emissions. Atmospheric pollution problems are geographically limited and also depend upon other variables such as time of day, and weather conditions. The major problems are associated with Southern California and other cities of the southwest, and congested urban areas. It is proposed that emissions standards should be made flexible in order to reflect these environmental variations, and thus to achieve the maximum environmental improvement for the least total cost to vehicle owners and users. Several “zoning” schemes are discussed, having the common feature that cars meeting the most rigorous standards would be required only in zones having the greatest density of vehicles and population (or the greatest propensity of “smog”). Such zones would probably be small enough in geographic extent to affect only a small fraction of vehicles--mainly taxis, delivery trucks and CBD commuters--at most 15% or so of the vehicles registered. Given the smaller number of vehicles involved, a fairly short (say 3 years) transition would probably be adequate.